Swedish Tree Line

A new thread at bender’s suggestion. Treelines are a climate indicator that I’ve paid attention to in the past as evidence that made sense to me about the relationship of modern and medieval climate. I’ve posted up threads in the past about tree lines in California being higher than at present in the MWP and Holocene Optimum; likewise in the Urals and Fennoscandia – see this Category for some prior posts. Reader Tom has sent in a news report that Swedish tree lines are at levels that are matching the Holocene Optimum.

“The tree line has moved by up to 200 meters (656 feet) in some places. Trees have not grown at such high levels for around 7,000 years,” Leif Kullman, a professor at Umeaa University’s department of ecology and environmental science, told AFP Tuesday.

I’ve read a number of articles by Kullman from about 15 years ago in which he noted that tree lines at that time had not responded to warming; he even wondered whether the local temperature records were accurate. Kullman’s website However the present situation appears to be different. The article goes on to say:

“The number of plants and animals in Swedish forests has grown 100 percent in the last 50 years,” Kullman said.

Usually we hear that climate change has all sorts of adverse results; I wonder if we’ll see about loud headlines about unprecedented increases in plants and animals in Swedish forests.

IPCC 4AR takes a very dismissive position towards treeline changes as a temperature indicator in its criticism of Hubert Lamb. They said that such vegetation change is “difficult to interpret in terms of accurate quantitative temperature influences” ant that it may result “from physical or biological systems that involve complex lags between forcing and response, as is the case for vegetation and glacier changes.” Because IPCC 4AR dismissed this class of evidence, they did not review the state of evidence from tree line change in various parts of the world – a review that is long overdue.

Notwithstanding the casual dismissal of this line of evidence by IPCC 4AR, I regard evidence of tree lines reaching Holocene levels as potentially legitimate evidence of warm climate and will pay close attention to Kullmann’s information as it comes along. If tree lines have reached Holocene Optimum levels in Sweden, but treelines in Siberia and California haven’t even reached MWP levels, it will pose a conundrum – but an interesting one. Let’s hope that people survey the evidence rather than cherry picking, but that may be hoping too much.

I would hasten to say that, if changing treelines demonstrate modern warmth, that would not disprove our criticisms of the Hockey Team reconstructions. They would remain as valid as criticisms of the Piltdown Mann or Enron accounting. Just because I don’t accept bad accounting from the Team doesn’t mean that I’m not open to some other form of evidence in this matter.
Another recent article on Swedish treelines is Jonas Bergman, Dan Hammarlund, Gina Hannon, Lena Barnekow, Barbara Wohlfarth, 2005. Deglacial vegetation succession and Holocene tree-limit dynamics in the Scandes Mountains, west-central Sweden: stratigraphic data compared to megafossil evidence Review of Palaeobotany and Palynology 134 (2005) 129– 151. They discuss Kullmann’s results stating:

The long-term Holocene vegetation development in the central part of the Scandes is known through radiocarbon dating of subfossil wood remains (megafossils) found above the present-day tree-limit (Lundqvist, 1959; Kullman, 1995, 1998b; Kullman and Kjallgren, 2000). …

This megafossil data-set includes almost 250 samples of Pinus sylvestris, Betula pubescens, and Alnus incana collected above the modern altitudinal forest-limit…. the tree-limit in the southern part of the Scandes has ascended by 100–130 m in response to warming during the 20th century (Kullman, 2001), whereas no significant vegetation response has been reported from southern Sweden.

Bergman et al 2005 Figure xx.

The figure of 200 m in the news article is greater than the figure of 100-130 m in the academic article. Above is a graphic from Bergman et al which shows that treelines 100-200 meters above 19th century treelines are not unprecedented since higher levels were achieved in the Holocene Optimum but a sustained 200 meter rise in treeline would indicate warmth exceeding medieval levels in this area.

Tree lines evidence best when the vegetation is in quasi-equilibrium with the climate (as in the Early Holocene), if there are rapid changes in climate, treeline elevations will lag because of the time required trees to establish.

Your text implies that this is not an adverse event. If you like pine forests this may be so, but for those interested in the conservation of the alpine vegetation, the invasion of trees is definitely adverse.

Subfossil samples of Scots pine (Pinus sylvestris) and evidence of pine stomata and pollen accumulation rates from previously studied lakes located beyond the present pine forest line in Finnish Lapland were used to reconstruct the extent of the past forest line and the corresponding minimum shift in mean July temperatures, compared with the present. The location of the present pine forest line follows the c. + 12.2C mean July temperature isoline (1961-1990). When minimum shifts in mean July temperatures during the Holocene were studied, the estimated glacio-isostatic land uplift and its regional differences were taken into account. Results indicate that pine reached its maximum distribution between 8300 and 4000 cal. yr BP. The inferred minimum shift in mean July temperature was at that time c. +2.5. Until 3000 cal. yr BP, the results indicate a shift of c. + 1°C. Between 2538 and 1721 cal. yr BP, evidence for a wider distribution of pine in Finnish Lapland is lacking. During the “Mediaeval Warm Period’ the reconstructed minimum shift in mean July temperature was +0.5. The record of subfossil pines beyond the present pine treeline ceases during the initiation of the “Little Ice Age’, c. 700 years ago.

Your text implies that this is not an adverse event. If you like pine forests this may be so, but for those interested in the conservation of the alpine vegetation, the invasion of trees is definitely adverse.

??? What if I like pines better than “alpine vegetation?” I didn’t think that any of this was a matter of personal preference.

But the real point is that everything changes…They’re all bent out of shape in Colorado because the quaking aspen forests seem to be dying, but never mind that many of them came about because of early logging and nature seems to be shifting back to its previous state.

Implied in the statement is that there is some “equilibrium” state that is supposed to exist. I don’t think this is the case.

Regarding current changes in treelines, could they not be due to a combination of changes in temp, precip and CO2 concs (as well as the specific species)? Unfortunately neither of the abstracts (in #2 and #3) get into these. Does anyone with access to the full papers know whether these were considered in the analysis and, if so, the rationale for why they are not part of the equation?

#4
Changes in precipitation of CO2 concentrations have an effect on tree ring widths and density, especially in semi-arid climates. But their impact on survivorship at the tree line will be limited in the cool moist climates of northern Fennoscandinavia.

I’m not sure what limits tree survivorship at the tree line here. If it is the drying winter winds then neither precipitation nor CO2 will help. If insufficient assimilation of carbon during the short summer causes mortality, then increasing CO2 levels may raise net primary productivity, but this effect is probably fairly small relative to any temperature response. This effect would be greater if the trees were water stressed.

I don’t think either paper considers C02 or precipitation impacts, but that’s entirely reasonable in this area.

#4
This is not just my opinion. Alpine environments are threatened by a number of factors and are a much higher conservation priority than young pine forests, of which there is no shortage in Scandinavia.

1. But doesn’t an advancing tree line also mean greater carbon sequestration? Isn’t that a good thing? Also, if the pine stands advance, wouldn’t alpine vegetation also advance, albeit at different speeds? [I’m trying to understand what will change and how.]

2. How does the threat to alpine vegetation from other factors compare with that due to warming alone (and over what time periods)? Understanding this will give us a clue as to the relative importance of the latter versus the former.

#7
In many cases the alpine vegetation is limited by the height of the mountain – they cannot go higher than that! Movement of alpine vegetation into the high alpine belt of rock and ice is likely to be slow as there is very little soil development here.

Increases in forest cover will increase carbon sequestration, which is a good thing. Unfortunately, there the reduction in albedo is likely to be far more significant. Snow falling in forests drops beneath the canopy, and here it can reflect far less incoming radiation than it can without tree cover.

Alpine vegetation in different areas is threatened by different factors. Tourism is a threat in some places, for example snow conditions are changed at downhill ski resorts. Tourism is probably more of a threat in the Alps than in Scandinavia. Introduced plants and animals can be a problem, especially in New Zealand. Acid rain and enhanced UV radiation following ozone loss are also potential threats, but have been less studied. Climate change is probably the single largest threat because of its geographic coverage.

The point that Steve and others made about the inappropriate use of bcp proxies is that the anomalous growth of bcps was not due to temp, because temps in that part of California have not increased much. So the question for the higher tree line in Sweden would seem to be whether it correlates with temp or not.

1. young trees do sequester C but do not utilize increased CO2 any differently . One of our ex-Presidents, Reagan, inadvertently supplied many with humor when misunderstanding this issue and proposed cutting old growth to better sequester C.

And as N is usu a limiting factor in tree stands for taking advantage of CO2 fert (esp in alpine tundra as little N is available), CO2 concs likely are not contributing to range spread wrt alleviating growth stress (your #5) or accelerate plant growth.

In fact, in the US we have just released a new climate zone chart for tree hardiness that shows the northward migration of plant climate zones, which is a result of temps migrating northward (not added C to the C cycle).

Steve mentioned a few weeks ago a USFS researcher’s studies of trees at treeline in the S Sierra. One of her conclusions was the drought culled the weakest trees and left the most fit. This is the way of the world. The most adaptable individuals are moving up – whether they are most adaptable to cold if some swing occurs remains to be seen at a scale we have difficulty observing (hence the ability to manipulate).

#2
My research on movement of the treeline in north central Canada found that most of the movement was by root growth expansion a much faster process. Seeds were produced and some sprouted but few survived. The critical factor appears to be the ability to trap and hold snow. The other factor often overlooked is the wind. It is also important to know there are trees growing north of the treeline, but they are ground hugging so that they have snow cover in the winter and stay out of the wind.

1.young trees do sequester C but do not utilize increased CO2 any differently . One of our ex-Presidents, Reagan, inadvertently supplied many with humor when misunderstanding this issue and proposed cutting old growth to better sequester C.

This is a generalization and dependence on sequstion and exchange is non-typical. In high latitudes, mature boreal forests are net emitters The main variables controlling the behaviour of the vegetation is the incoming photosynthetically active photon flux density (PPFD), temperature, soil mositure and vapor pressure deficit (VPD, defined as the difference between the saturated water vapor pressure and the actual water vapor pressure at a given temperature in the atmosphere).

PPFD is the most immediate environmental control on photosynthesis (Malhi et al., 1999). The major influence of temperature on net carbon balance is through its effects on rates of both autotrophic and heterotrophic respirations (Malhi et al., 1999). Since we can not distinguish between these two types, we may only describe the net effect of respiration. Vapor pressure deficit controls stomatal closure, thus it has a direct effect on the rate of photosynthesis. High VPD causes stomatal closure, decreasing photosynthesis (Anthoni et al., 1999). Lack of soil moisture also reduces carbon uptake by causing stomatal closure, but also affects soil carbon and nutrient release by restricting microbial decomposition (Malhi et al., 1999).

And as N is usu a limiting factor in tree stands for taking advantage of CO2 fert (esp in alpine tundra as little N is available), CO2 concs likely are not contributing to range spread wrt alleviating growth stress (your #5) or accelerate plant growth.

Especially in alpine tundra. Um ..tundra is derived from the Finnish word for treeless so we would not expect many trees there.

N2 being around 78% of the gaseous atmospheric envelope ,is supplied at around 4% concentration in rain. Plant utilization of N2 is entirely dependent on the rhizosphere and the symbiotic constituent micro flora.

#15. in our E&E article, we cited some references on high-altitude nitrate fertilization in connection with bristlecones, as well as possible CO2 fertilization. In order for the Mannians to assert that bristlecones were a temperature proxy, all fertilization effects have to be analyzed. THe NAS panel also issued a caveat on nitrate fertilization. Industrial pollution has led to much much higher nitrates deposition in high altitudes. MAybe that’s a factor in Europe.

That would be dependent on the soil rhizosphere and mycorrhizae,utilisation would be dependent on the soils.In an increased soluble environment such as the high altitude vegetation,increased N2 fertilisation would be expected.

In addition the increased fire suppression regime we are seeing now,would also see decreased phospherus by forest fire,which destroys the mycorrhizae nitrogen nodulators for symbiotic forest root growth.So we can see different growth regimes within localities

You are correct,without all details of the particular biospheric and environmental parameters for the locality it would be difficult,to structure a growth profile.

Dano, you claim that increasing CO2 does not accelerate plant growth, and as is far too common with you, your citation is a press release wherein the claim is made, not by the scientist, but by the journalist. There is abundant evidence that increasing CO2 does increase plant growth, especially in water-limited areas. Commercial greenhouse operators routinely increase CO2 levels in their greenhouses for this very reason.

The journalist misunderstands the situation so completely that in addition to the error about increasing growth, she produced this howler:

Previous research has also shown that the doubling of atmospheric carbon dioxide expected to occur this century can cause leaf stomata to close by 20 to 40 percent in diverse plant species, thus reducing carbon dioxide intake.

1. So the short answer to the issue posed in #5 is that an advancing treeline for a particular species does not necessarily reflect higher temps. It could also reflect changes in precip, CO2 concs, and biologically-available nitrogen (and other nutrients), and even winds (and, perhaps, factors affecting competition for nutrients between advancing/retreating species). Presumably the papers themselves, or the papers they cite, would address why and at what level of confidence the changes in treeline might reflect temps. Which brings me back to the original query posted in #5: Does anyone with access to the full papers know whether these were considered in the analyses and, if so, the rationale for focusing on warming rather than (some combination of) these other factors?

2. Presumably, the same set of factors enumerated above would also affect the ability to use tree ringwidths and densities as proxies.

Tree lines evidence best when the vegetation is in quasi-equilibrium with the climate (as in the Early Holocene), if there are rapid changes in climate, treeline elevations will lag because of the time required trees to establish.

Your text implies that this is not an adverse event. If you like pine forests this may be so, but for those interested in the conservation of the alpine vegetation, the invasion of trees is definitely adverse.

I propose a debate to determine the time of the Best of All Possible Worlds so we can distinguish between “good” and “bad” Climate change. It seems to me that the debate has a unstated major premise that X (for X insert the year of your birth) had the best possible climate and therefore any change is a worsening of the world. I must be incredibly blessed and cursed to have lived in the best possible climate and now I face a inevitable deviation from that glorious time. What we need is a Carl Wunderlich for the globe.

At the Climate Seminar at KTH in Stockholm in September I met a Finnish historian who had examined their tax records. Several ( I can’t remember exactly how many) hundred years ago wooden barrel makers 300 km north of where oak trees now grow were paying tax on the oak barrels they made.

There is NO doubt about CO2 increasing plant growth. I have recently done some eningering studies for a lerge greenhouse. They currently spend ~$500,000 pa for natural gas that they burn purely to increase CO2 levels to about 900 ppm. This increases plant growth by 30-40% WITHOUT AN INCREASE IN THE NEED FOR WATER. They reckon that the recent increase in CO2 has increased growth by about 5% – again without a need for more water. Perhaps that is why forested area is expanding and deserts are decreasing.

In addition higher then usual levels of nitrates from industrial areas in bordering countries can be seen in soil levels.This would suggest again elevated levels of N2 fertilization and assimilation.

2 State controls of silviculture in Sweden

Northern Sweden was very sparsely populated until the beginning of the 19th century. At that time an accelerating agrarian colonization took place, and later during that century a large-scale exploitation of the virgin forest began. The first forest resources to be exploited were those close to the Bothnian coast, and subsequently exploitation moved further inland. This exploitation affected almost all forest land in northern Sweden during the period 1850-1950.

In many areas of northern Sweden forest inventories preceded exploitation. They were often carried out as tree counts, i.e. measurements of large diameters trees as well as an estimation of their saw-timber quality. This inventories can, together with more accurate inventories carried out at a later time, be used to estimate the standing volume as well as tree diameter distribution in the unexploited forest. In some cases the number of dead standing trees was also recorded.

The exploitation of the forest meant that in most areas the average standing volume of trees was drastically lowered before any forest cultivation and stand treatment began. In two areas in the southern part of the boreal forest the standing volume of today is 25% to 40 % lower than it was before any exploitation had taken place. Forest surveys, from 1870, of northern Sweden show a similar pattern, although this material also includes forests that had already been exploited to some extent when the first inventories were made. The standing volume of today is less than it was 120 years ago despite the more intensive forest cultivation and management practices of the latest decades. http://www.borealforest.org/world/world_sweden.htm

Selective logging of higher diameter trees allows more light through the forest canopy and faster growth.Spread of the seeded areas ,and faster growth even in mature areas.

In 1982, several rectangular slots were cut for regeneration in an old sub-alpine spruce forest stand. The slant openings, with a north-east / south-west orientation on the steep, north aspect created rapid environmental changes to the border trees. Possible reactions of these border trees compared to check trees within the closed canopy stand were analyzed in 1997.

The sub-alpine Norway spruce stands of ages around 100 years, usually considered slow growing on a north aspect, still seem capable of reaction to sudden light changes.

#24
Increased CO2 concentrations does increase plant water use efficiency as they need open their stomata for a shorter time to get the same amount of carbon, and so lose less water. But this only applies when the plants are photosynthesizing. Below ~5°C, most plants stop photosynthesis, so this effect is not important at cold temperatures.

At low temperatures some water is still lost by the plants, especially if ice crystals whipped up by high winds damage the cuticle.

If the soil is frozen, the plant cannot replenish this lost water, and so experience physiological drought, even in moist climates, which can lead to death of all or part of the plant.

Wow. A thread I like, with people containing knowledge about natural processes.

15:

Your excellent reply still does not change the import of my answer, necessarily limited by comment threads. I would say VPD in your 1. is the reason for small caliper and relative ‘dwarfing’ in hi lats, in addition to length of growing season. Anyway, there is no net C sequestration and my approach was scalar along ecological lines. And allow me to correct and say ‘taiga invading to tundra’.

20:

Indur:

The American Arbor Day Foundation just released it’s new tree hardiness map. The zones have moved north. Because of temperature, not N deposition, which has different effects on physiology. It’s a nice wish you have, though.

22:

There is NO doubt about CO2 increasing plant growth.

Sure there is. Go to a good uni library and look up the FACE studies. Report back to us and share what you found that contradicts your assertion, esp for persons using non-nutirent limited greenhouses as a proxy for ecosystems.

23:

There is evidence in the US that calcareous soils are problematic to N2 dep, and Al+++ makes assessment difficult**, and stream runoff tells the tale, but the assertion that N dep is a net plus to growth is a surprise, and against many principles of ecology, esp wrt location and climatic gradients.

And although your gap dynamics story in 23 is fancy, it doesn’t pertain to long-lived trees used in dendro studies, where gap dynamics usu. aren’t pertaining.

25:

It’s rare when you read such a well-done answer here. Thank you.

Best,

D

** Further evidence that Tim Ball’s claims that sugar maple didn’t decline due to acid rain are cr*p.

Sure there is. Go to a good uni library and look up the FACE studies. Report back to us and share what you found that contradicts your assertion, esp for persons using non-nutirent limited greenhouses as a proxy for ecosystems.

Bull. Here are summaries of all sorts of FACE studies, showing increasing growth. Here’s a summary of studies on pines.